Chapter Four

Shading Devices

Chapter Four

Shading Devices

1

1. Introduction.2. Types of shading devices.3. Various Shading Devices and their Geometries.4. Design of shading devices.5. Overheated and underheated periods.6. Using the Effective Temperature Nomogram.7. The Hourly Temperature Calculator.8. When Is Shading Required?9. Sun-Shading Periods.10. Determination of the sun's position.11. Superimposing the sun-shading periods.12. The shadow angle protractor.13. Examples of shading devices.14. Tests and Exrecises.15. References.

1. Introduction.

Windows may contain several elements including shading devices. The design of these elementsreflect various functions including thermal control. There are three types of shading devices - vertical,horizontal and egg-crate. The design of sunshading devices for thermal comfort involves four steps:determination of when shading is required; determination of the position of the sun at the timeswhen shading is required; determination of the dimensions and proportions of the required shadingdevice and finally the architectural and structural design of the shading device.

Windows may contain several elements including shading devices. The design of these elementsreflect various functions including thermal control. There are three types of shading devices - vertical,horizontal and egg-crate. The design of sunshading devices for thermal comfort involves four steps:determination of when shading is required; determination of the position of the sun at the timeswhen shading is required; determination of the dimensions and proportions of the required shadingdevice and finally the architectural and structural design of the shading device.

There are three types of sun-shading devices.They are:

Windows without shading devices have someshading characteristics measured by theirhorizontal and vertical shading angles. See figure1. In describing the characteristics of shadingdevices it should be noted that the window andthe shading device are considered as one unit.

Vertical Shading Devices consist of pilasters,louvre blades or projecting fins in a verticalposition. Their performance is measured by the

horizontal shadow angle (delta). They arecommonly referred to as fins and are mosteffective on western and eastern elevations. Seefigure 2.

Horizontal Shading Devices are usually in theform of canopies, long verandas, movablehorizontal louvre blades or roof overhangs. Theyare best suited to southern and northernelevations and their performance is measured by

the vertical shadow angle (epsilon). See figure3.

Are combinations of vertical and horizontaldevices. They are usually in the form of grillblocks or decorative screens. Their performanceis determined by both the horizontal and vertical

shadow angles and (delta and epsilon). Seefigure 4.

There are certain steps to be followed in thedesign of shading devices.

It is necessary to determine when shading isrequired, that is at what times of the year andduring what hours of the day. This is usually doneby defining the overheated and underheated

Vertical Shading Devices.

Horizontal Shading Devices.

Egg-Crate Devices.

Step One:

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2. Types of Shading Devices.

Openings, especially windows, greatly influencethe thermal conditions within a building.Windows usually contain several elements,some of which are adjustable. These elementsperform various functions, including thefollowing:

External shading devices are only one of theseelements. Others include curtains, glass, solid orlouvered shutters, security bars and mosquitoscreens. The functions of external shadingdevices include:

It can be seen from the above that the design ofopenings can be very complex indeed. We shallconcentrate on the design of external shadingdevices but it can also be seen that the design ofthese devices should enable them function inseveral ways. We shall therefore narrow downour aim to the design of external shading devicesfor thermal comfort.

In warm -humid areas, such as Lagos andCalabar, it is often desirable to exclude the sunthroughout the year. There are however, otherregions with composite climates, with distincthot and cold seasons. The design of externalshading devices in such areas must exclude solarradiation in the hot season and allowprogressively greater quantities of solar radiationto enter as the season becomes colder.

-ventilation-daylighting-provision of privacy and security-prevention of glare-exclusion of rainfall-allowing a view out-exclusion of dust, noises, pollution andinsects-exclusion of direct solar radiation.

-allowing a view out-protection from rain-protection from direct solar radiation-protection from sky glare

Openings, especially windows, greatly influencethe thermal conditions within a building.Windows usually contain several elements,some of which are adjustable. These elementsperform various functions, including thefollowing:

External shading devices are only one of theseelements. Others include curtains, glass, solid orlouvered shutters, security bars and mosquitoscreens. The functions of external shadingdevices include:

It can be seen from the above that the design ofopenings can be very complex indeed. We shallconcentrate on the design of external shadingdevices but it can also be seen that the design ofthese devices should enable them function inseveral ways. We shall therefore narrow downour aim to the design of external shading devicesfor thermal comfort.

In warm -humid areas, such as Lagos andCalabar, it is often desirable to exclude the sunthroughout the year. There are however, otherregions with composite climates, with distincthot and cold seasons. The design of externalshading devices in such areas must exclude solarradiation in the hot season and allowprogressively greater quantities of solar radiationto enter as the season becomes colder.

2

Figure 1: Shading characteristics of a simple window.Shading chart indicating the areas of the sky which areshaded by the thickness of the wall.

3. Various Shading Devices and

Their Geometries.

4. Design of Shading Devices.

There are three types of sun-shading devices.They are:

Windows without shading devices have someshading characteristics measured by theirhorizontal and vertical shading angles. See figure1. In describing the characteristics of shadingdevices it should be noted that the window andthe shading device are considered as one unit.

Vertical Shading Devices consist of pilasters,louvre blades or projecting fins in a verticalposition. Their performance is measured by the

horizontal shadow angle (delta). They arecommonly referred to as fins and are mosteffective on western and eastern elevations. Seefigure 2.

Horizontal Shading Devices are usually in theform of canopies, long verandas, movablehorizontal louvre blades or roof overhangs. Theyare best suited to southern and northernelevations and their performance is measured by

the vertical shadow angle (epsilon). See figure3.

Are combinations of vertical and horizontaldevices. They are usually in the form of grillblocks or decorative screens. Their performanceis determined by both the horizontal and vertical

shadow angles and (delta and epsilon). Seefigure 4.

There are certain steps to be followed in thedesign of shading devices.

It is necessary to determine when shading isrequired, that is at what times of the year andduring what hours of the day. This is usually doneby defining the overheated and underheated

Vertical devices.Horizontal devices.Egg-crate devices.

Vertical Shading Devices.

Horizontal Shading Devices.

Egg-Crate Devices.

Step One:

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There are three types of sun-shading devices.They are:

Windows without shading devices have someshading characteristics measured by theirhorizontal and vertical shading angles. See figure1. In describing the characteristics of shadingdevices it should be noted that the window andthe shading device are considered as one unit.

Vertical Shading Devices consist of pilasters,louvre blades or projecting fins in a verticalposition. Their performance is measured by the

horizontal shadow angle (delta). They arecommonly referred to as fins and are mosteffective on western and eastern elevations. Seefigure 2.

Horizontal Shading Devices are usually in theform of canopies, long verandas, movablehorizontal louvre blades or roof overhangs. Theyare best suited to southern and northernelevations and their performance is measured by

the vertical shadow angle (epsilon). See figure3.

Are combinations of vertical and horizontaldevices. They are usually in the form of grillblocks or decorative screens. Their performanceis determined by both the horizontal and vertical

shadow angles and (delta and epsilon). Seefigure 4.

There are certain steps to be followed in thedesign of shading devices.

It is necessary to determine when shading isrequired, that is at what times of the year andduring what hours of the day. This is usually doneby defining the overheated and underheated

Vertical Shading Devices.

Horizontal Shading Devices.

Egg-Crate Devices.

Step One:

�

�

� �

Openings, especially windows, greatly influencethe thermal conditions within a building.Windows usually contain several elements,some of which are adjustable. These elementsperform various functions, including thefollowing:

External shading devices are only one of theseelements. Others include curtains, glass, solid orlouvered shutters, security bars and mosquitoscreens. The functions of external shadingdevices include:

It can be seen from the above that the design ofopenings can be very complex indeed. We shallconcentrate on the design of external shadingdevices but it can also be seen that the design ofthese devices should enable them function inseveral ways. We shall therefore narrow downour aim to the design of external shading devicesfor thermal comfort.

In warm -humid areas, such as Lagos andCalabar, it is often desirable to exclude the sunthroughout the year. There are however, otherregions with composite climates, with distincthot and cold seasons. The design of externalshading devices in such areas must exclude solarradiation in the hot season and allowprogressively greater quantities of solar radiationto enter as the season becomes colder.

3

Figure 2: A vertical shading device. Shading chart indicatingthe additional areas of the sky which are shaded by avertical shading device on one side of the window only.

periods.

The position of the sun at the times whenshading is required must be established. This isusually done with the aid of a sun-path diagram.

The dimensions and proportions of the shadingdevice that will provide shading during theperiod earlier defined is found. This is done withthe aid of a shadow angle protractor.

The choice of prefabricated devices or thedesign of new ones. The design of shadingdevices takes not only the required geometryinto consideration but also aesthetic andstructural factors.

Step Two:

Step Three:

Step Four:

periods.

The position of the sun at the times whenshading is required must be established. This isusually done with the aid of a sun-path diagram.

The dimensions and proportions of the shadingdevice that will provide shading during theperiod earlier defined is found. This is done withthe aid of a shadow angle protractor.

The choice of prefabricated devices or thedesign of new ones. The design of shadingdevices takes not only the required geometryinto consideration but also aesthetic andstructural factors.

Step Two:

Step Three:

Step Four:

The thermal stress experiencedin a pa r t i cu l a r c i t y i scharacterised by the durationof the overheated, thec o m f o r t a b l e a n d t h eunderheated periods. Theoverheated period is thatperiod when there is hotd i s c o m f o r t w h i l e t h eunderheated period representscold discomfort. In compositeclimates, there are certainperiods of the year, especiallyduring the harmattan monthsof November to February,when there is underheatingc h a r a c t e r i s e d b y l o wtemperatures in the nights andearly mornings. The use of solarradiation during this period iswelcome. On the other hand,there is serious overheating fora few weeks in March/Apriland exclusion of sunlight isdesirable at this period. Thesame shading device is used toallow solar heating during theunderheated period and blockout the sun during theoverheated per iod. Thegeometry of the shading devicemust therefore be determinedon the basis of the duration oft h e o v e r h e a t e d a n dunderheated periods and whenthey occur during the year.

T h e o v e r h e a t e d a n dunderheated periods aredetermined with the aid of athermal index. Such an indexshould be able to indicate forgiven climatic conditionsw h e t h e r t h e r e i s c o l ddiscomfort, comfort or hotdiscomfort. This process isexplained with the aid of the

4

Figure 4: A shading device with vertical and horizontalelements. Shading chart indicating the additional areas of thesky shaded by a combination of horizontal and verticalprojections.

Figure 3: A horizontal shading device. Note that it projectsbeyond the window on plan to prevent the sun reaching thewindow from the ends of the shading device. Shading chartindicating the additional areas of the sky which are shaded bya horizontal shading device.

periods.

The position of the sun at the times whenshading is required must be established. This isusually done with the aid of a sun-path diagram.

The dimensions and proportions of the shadingdevice that will provide shading during theperiod earlier defined is found. This is done withthe aid of a shadow angle protractor.

The choice of prefabricated devices or thedesign of new ones. The design of shadingdevices takes not only the required geometryinto consideration but also aesthetic andstructural factors.

Step Two:

Step Three:

Step Four:

5. Overheated and

Underheated

Periods.

The thermal stress experiencedin a pa r t i cu l a r c i t y i scharacterised by the durationof the overheated, thec o m f o r t a b l e a n d t h eunderheated periods. Theoverheated period is thatperiod when there is hotd i s c o m f o r t w h i l e t h eunderheated period representscold discomfort. In compositeclimates, there are certainperiods of the year, especiallyduring the harmattan monthsof November to February,when there is underheatingc h a r a c t e r i s e d b y l o wtemperatures in the nights andearly mornings. The use of solarradiation during this period iswelcome. On the other hand,there is serious overheating fora few weeks in March/Apriland exclusion of sunlight isdesirable at this period. Thesame shading device is used toallow solar heating during theunderheated period and blockout the sun during theoverheated per iod. Thegeometry of the shading devicemust therefore be determinedon the basis of the duration oft h e o v e r h e a t e d a n dunderheated periods and whenthey occur during the year.

T h e o v e r h e a t e d a n dunderheated periods aredetermined with the aid of athermal index. Such an indexshould be able to indicate forgiven climatic conditionsw h e t h e r t h e r e i s c o l ddiscomfort, comfort or hotdiscomfort. This process isexplained with the aid of the

The thermal stress experiencedin a pa r t i cu l a r c i t y i scharacterised by the durationof the overheated, thec o m f o r t a b l e a n d t h eunderheated periods. Theoverheated period is thatperiod when there is hotd i s c o m f o r t w h i l e t h eunderheated period representscold discomfort. In compositeclimates, there are certainperiods of the year, especiallyduring the harmattan monthsof November to February,when there is underheatingc h a r a c t e r i s e d b y l o wtemperatures in the nights andearly mornings. The use of solarradiation during this period iswelcome. On the other hand,there is serious overheating fora few weeks in March/Apriland exclusion of sunlight isdesirable at this period. Thesame shading device is used toallow solar heating during theunderheated period and blockout the sun during theoverheated per iod. Thegeometry of the shading devicemust therefore be determinedon the basis of the duration oft h e o v e r h e a t e d a n dunderheated periods and whenthey occur during the year.

T h e o v e r h e a t e d a n dunderheated periods aredetermined with the aid of athermal index. Such an indexshould be able to indicate forgiven climatic conditionsw h e t h e r t h e r e i s c o l ddiscomfort, comfort or hotdiscomfort. This process isexplained with the aid of the

5

Figure 5: The Effective Temperature nomogram for persons wearing normalclothes.

Effective Temperature index using Zaria as anexample.

The climatic data needed are the monthlyminima and maxima of dry-bulb and wet-bulbtemperatures as well as the mean monthly windvelocity. The wet-bulb temperatures are notalways available and in such a case they shouldbe calculated from the monthly minima andmaxima of relative humidity. This was done forZaria with the aid of the psychometric chart. Seetable 1. Alternatively, the computer programPSYCHRO may be used. See chapter 12.

The Effective Temperature nomogram is used toobtain the Effective Temperatures. In theexample, the nomogram for persons wearingnormal business clothing is used and an airvelocity of 1.0 m/s is assumed. The maximumDBT and the maximum WBT are used to obtainthe maximum ET while the minimum DBT andthe minimum WBT are used to obtain theminimum ET. The computer program EFFECTmay be used for this purpose.

We have now obtained the monthly minima andmaxima of Effective Temperature. The comfortlimits 22 -27 degrees Celsius are provisionallyassumed for the Effective Temperature index inNigeria. The calculated Effective Temperatureshould be compared with the comfort limits todetermine the thermal stress and hence theperiod when shading is required.

The hourly temperature calculator is used todetermine the diurnal temperature variation. Seefigure 6. It is based on the sinusoidal character oftemperature variation with the minimumtemperature around 6.00 am and the maximumaround 2.00 pm. To use the hourly temperaturecalculator, the minimum and maximumtemperatures are marked. These two points arejoined by a straight line and results are read offthe line. For example, given a minimumtemperature of 20 degrees Celsius and a

6. Using the Effective

Temperature Nomogram.

7. The Hourly Temperature

Calculator.

Effective Temperature index using Zaria as anexample.

The climatic data needed are the monthlyminima and maxima of dry-bulb and wet-bulbtemperatures as well as the mean monthly windvelocity. The wet-bulb temperatures are notalways available and in such a case they shouldbe calculated from the monthly minima andmaxima of relative humidity. This was done forZaria with the aid of the psychometric chart. Seetable 1. Alternatively, the computer programPSYCHRO may be used. See chapter 12.

The Effective Temperature nomogram is used toobtain the Effective Temperatures. In theexample, the nomogram for persons wearingnormal business clothing is used and an airvelocity of 1.0 m/s is assumed. The maximumDBT and the maximum WBT are used to obtainthe maximum ET while the minimum DBT andthe minimum WBT are used to obtain theminimum ET. The computer program EFFECTmay be used for this purpose.

We have now obtained the monthly minima andmaxima of Effective Temperature. The comfortlimits 22 -27 degrees Celsius are provisionallyassumed for the Effective Temperature index inNigeria. The calculated Effective Temperatureshould be compared with the comfort limits todetermine the thermal stress and hence theperiod when shading is required.

The hourly temperature calculator is used todetermine the diurnal temperature variation. Seefigure 6. It is based on the sinusoidal character oftemperature variation with the minimumtemperature around 6.00 am and the maximumaround 2.00 pm. To use the hourly temperaturecalculator, the minimum and maximumtemperatures are marked. These two points arejoined by a straight line and results are read offthe line. For example, given a minimumtemperature of 20 degrees Celsius and a

maximum of 30 degrees Celsius, thetemperature at 12 noon is about 28.5 degreesCelsius and the temperature rises to 26 degreesCelsius at 10.00 a.m. and falls back to the same26 degrees Celsius at about 6.40 pm.

It is possible to construct a complete effectivetemperature isopleth showing the underheated,comfortable and overheated periods using thehourly temperature calculator and thecalculated effective temperatures. For ourpurposes however, it is usually enough todetermine when shading should start and whenit should stop.

8. When Is Shading Required?

Shading is required both during the overheatedperiod and when conditions are comfortable.The reason for this is that if solar gain is permittedduring comfortable periods the excess heat thusgained may cause hot discomfort. Thus thelower limit of comfort is used to establish when

6

Figure 6: The hourly temperature calculator.

Effective Temperature index using Zaria as anexample.

The climatic data needed are the monthlyminima and maxima of dry-bulb and wet-bulbtemperatures as well as the mean monthly windvelocity. The wet-bulb temperatures are notalways available and in such a case they shouldbe calculated from the monthly minima andmaxima of relative humidity. This was done forZaria with the aid of the psychometric chart. Seetable 1. Alternatively, the computer programPSYCHRO may be used. See chapter 12.

The Effective Temperature nomogram is used toobtain the Effective Temperatures. In theexample, the nomogram for persons wearingnormal business clothing is used and an airvelocity of 1.0 m/s is assumed. The maximumDBT and the maximum WBT are used to obtainthe maximum ET while the minimum DBT andthe minimum WBT are used to obtain theminimum ET. The computer program EFFECTmay be used for this purpose.

We have now obtained the monthly minima andmaxima of Effective Temperature. The comfortlimits 22 -27 degrees Celsius are provisionallyassumed for the Effective Temperature index inNigeria. The calculated Effective Temperatureshould be compared with the comfort limits todetermine the thermal stress and hence theperiod when shading is required.

The hourly temperature calculator is used todetermine the diurnal temperature variation. Seefigure 6. It is based on the sinusoidal character oftemperature variation with the minimumtemperature around 6.00 am and the maximumaround 2.00 pm. To use the hourly temperaturecalculator, the minimum and maximumtemperatures are marked. These two points arejoined by a straight line and results are read offthe line. For example, given a minimumtemperature of 20 degrees Celsius and a

maximum of 30 degrees Celsius, thetemperature at 12 noon is about 28.5 degreesCelsius and the temperature rises to 26 degreesCelsius at 10.00 a.m. and falls back to the same26 degrees Celsius at about 6.40 pm.

It is possible to construct a complete effectivetemperature isopleth showing the underheated,comfortable and overheated periods using thehourly temperature calculator and thecalculated effective temperatures. For ourpurposes however, it is usually enough todetermine when shading should start and whenit should stop.

8. When Is Shading Required?

Shading is required both during the overheatedperiod and when conditions are comfortable.The reason for this is that if solar gain is permittedduring comfortable periods the excess heat thusgained may cause hot discomfort. Thus thelower limit of comfort is used to establish when

maximum of 30 degrees Celsius, thetemperature at 12 noon is about 28.5 degreesCelsius and the temperature rises to 26 degreesCelsius at 10.00 a.m. and falls back to the same26 degrees Celsius at about 6.40 pm.

It is possible to construct a complete effectivetemperature isopleth showing the underheated,comfortable and overheated periods using thehourly temperature calculator and thecalculated effective temperatures. For ourpurposes however, it is usually enough todetermine when shading should start and whenit should stop.

8. When Is Shading Required?

Shading is required both during the overheatedperiod and when conditions are comfortable.The reason for this is that if solar gain is permittedduring comfortable periods the excess heat thusgained may cause hot discomfort. Thus thelower limit of comfort is used to establish when

7

Location: Year: Lat. & Long. Nomogram ET or CET Comfort limits

Zaria 1969 - 197511 08 N

7 41’ E

Normalclothing

Lower: 22 C Upper: 27 C

Notes: Air velocity assumed.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Mean air velocity (m/s) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Mean maximum DBT ( C) 29.7 33.7 36.3 36.5 34.1 31.8 29.0 28.4 29.6 32.1 31.6 30.4

Mean min RH (%) 16 13 16 27 37 52 64 68 62 39 20 19

Mean max WBT( C) 14.4 15.9 18.3 21.5 22.4 23.4 23.6 23.4 23.4 21.3 16.4 15.5

Maximum ET( C) 21.4 23.5 25.4 26.7 26.2 25.7 24.4 24.0 26.6 24.9 22.9 22.0

Mean min DBT( C) 13.6 16.5 20.3 22.8 22.1 21.0 20.1 19.8 19.8 19.0 15.0 13.4

Mean max RH(%) 38 32 44 68 84 90 94 96 94 81 53 46

Mean min WBT( C) 7.0 8.5 13.1 18.1 19.9 19.8 19.3 18.8 18.6 16.8 10.1 7.8

Minimum ET ( C) 9.4 12.0 15.6 18.6 18.8 17.9 17.0 16.6 16.6 15.5 10.9 9.3

Shading start N 12:00 10:30 09:15 09:15 09:45 10:30 11:00 10:30 10:45 13:00 N

Shading stop N 16:15 18:00 20:00 19:45 19:00 18:00 17:30 18:00 17:45 15:30 N

Table 1: Sunshading periods using the Effective Temperature nomogram for Zaria.Note: F = full shading required, N = no shading required.

8

shading should start.

Take the minimum and maximum EffectiveTemperatures for January. Using a lower comfortlimit of 22 degrees Celsius, determine the time ofthe day when the temperature rises to 22degrees Celsius. This represents when shadingshould start. Shading should stop when thetemperature falls back to 22 degrees Celsius.When the temperature is always above thelower comfort limit then full shading is requiredthroughout. Consequently, when thetemperature is always below the lower comfortlimit no shading is required. See table 1. Repeatthe process for the remaining months of the yearand tabulate the data. If required, plot thesunshading periods thus obtained on a graph.

The sunshading periods can be obtained frombasic climatic data using the computer programSHADE. Plots of the thermal stress (overheatedand underheated periods) are made by thecomputer program COLDHOT. An example ofsuch a plot is presented in figure 7.

The next step in the design of sun-shadingdevices is to determine the position of the sun atthe times when shading is required. The positionof the sun is defined by two angles -the solaraltitude ß (beta, measured from 0 to 90 degreesabove the horizon) and the solar azimuth Θ(theta). The solar azimuth is measured from thesouth and is measured from 0 to -180 degrees(westward) and 0 to +180 degrees (eastward).See figure 8. The position of the sun can bedetermined in five ways:

The solar azimuth and altitude can be calculatedgiven the latitude, date and time frommathematical formulae. In fact the vertical andhorizontal shading angles can be calculateddirectly for various orientations. This method isusually too tedious for architectural purposes.

There are various computer programs that can

10.1 By Calculation.

10.2 By a computer program.

Fig

ure

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9

shading should start.

Take the minimum and maximum EffectiveTemperatures for January. Using a lower comfortlimit of 22 degrees Celsius, determine the time ofthe day when the temperature rises to 22degrees Celsius. This represents when shadingshould start. Shading should stop when thetemperature falls back to 22 degrees Celsius.When the temperature is always above thelower comfort limit then full shading is requiredthroughout. Consequently, when thetemperature is always below the lower comfortlimit no shading is required. See table 1. Repeatthe process for the remaining months of the yearand tabulate the data. If required, plot thesunshading periods thus obtained on a graph.

The sunshading periods can be obtained frombasic climatic data using the computer programSHADE. Plots of the thermal stress (overheatedand underheated periods) are made by thecomputer program COLDHOT. An example ofsuch a plot is presented in figure 7.

The next step in the design of sun-shadingdevices is to determine the position of the sun atthe times when shading is required. The positionof the sun is defined by two angles -the solaraltitude ß (beta, measured from 0 to 90 degreesabove the horizon) and the solar azimuth Θ(theta). The solar azimuth is measured from thesouth and is measured from 0 to -180 degrees(westward) and 0 to +180 degrees (eastward).See figure 8. The position of the sun can bedetermined in five ways:

The solar azimuth and altitude can be calculatedgiven the latitude, date and time frommathematical formulae. In fact the vertical andhorizontal shading angles can be calculateddirectly for various orientations. This method isusually too tedious for architectural purposes.

There are various computer programs that can

9. Sun-Shading Periods.

10. Determination of the sun's

position.

10.1 By Calculation.

10.2 By a computer program.

shading should start.

Take the minimum and maximum EffectiveTemperatures for January. Using a lower comfortlimit of 22 degrees Celsius, determine the time ofthe day when the temperature rises to 22degrees Celsius. This represents when shadingshould start. Shading should stop when thetemperature falls back to 22 degrees Celsius.When the temperature is always above thelower comfort limit then full shading is requiredthroughout. Consequently, when thetemperature is always below the lower comfortlimit no shading is required. See table 1. Repeatthe process for the remaining months of the yearand tabulate the data. If required, plot thesunshading periods thus obtained on a graph.

The sunshading periods can be obtained frombasic climatic data using the computer programSHADE. Plots of the thermal stress (overheatedand underheated periods) are made by thecomputer program COLDHOT. An example ofsuch a plot is presented in figure 7.

The next step in the design of sun-shadingdevices is to determine the position of the sun atthe times when shading is required. The positionof the sun is defined by two angles -the solaraltitude ß (beta, measured from 0 to 90 degreesabove the horizon) and the solar azimuth Θ(theta). The solar azimuth is measured from thesouth and is measured from 0 to -180 degrees(westward) and 0 to +180 degrees (eastward).See figure 8. The position of the sun can bedetermined in five ways:

The solar azimuth and altitude can be calculatedgiven the latitude, date and time frommathematical formulae. In fact the vertical andhorizontal shading angles can be calculateddirectly for various orientations. This method isusually too tedious for architectural purposes.

There are various computer programs that can

10.1 By Calculation.

10.2 By a computer program.Figure 8: Solar angles for vertical, sloping and horizontalsurfaces.

m a k e t h e n e c e s s a r ycalculations and present theresults graphically, sometimeseven in the form of plots. Suchprograms are now available onmicrocomputers and arebecoming more popular.

A good alternative is the use ofalmanacs where the necessarysolar angles are tabled. Thesetables undergo minor revisionsyearly.

Complex and lengthy researchon the sun-earth relationship iso f t e n c a r r i e d o u texperimentally using theheliodon, the solarscope orsome other device. See figure9. These studies are carried outon models and are verypopular in teaching.

T h e s e a r e g r a p h i c a lr ep re sen t a t i on s o f t hemovement of the sun acrossthe sky throughout the day andthe year. They owe theirpopularity to simplicity. Thesun-path diagram is used in thistext and is described in moredetail.

The sunpath diagram is aprojection of the hemisphere ofthe sky. The observer isassumed to be in the centre ofthis hemisphere and the sun totravel on the surface of thehemisphere. There are twotypes of projections used toobtain sun-path diagrams. Thef i rs t i s a stereographicprojection of the hemisphereonto a horizontal circle. This isthe most common projectionand is most useful in visualizingthe movement of the sun

10.3 From tables:

10.4 Experimental

methods:

10.5 Sun-path diagrams:

m a k e t h e n e c e s s a r ycalculations and present theresults graphically, sometimeseven in the form of plots. Suchprograms are now available onmicrocomputers and arebecoming more popular.

A good alternative is the use ofalmanacs where the necessarysolar angles are tabled. Thesetables undergo minor revisionsyearly.

Complex and lengthy researchon the sun-earth relationship iso f t e n c a r r i e d o u texperimentally using theheliodon, the solarscope orsome other device. See figure9. These studies are carried outon models and are verypopular in teaching.

T h e s e a r e g r a p h i c a lr ep re sen t a t i on s o f t hemovement of the sun acrossthe sky throughout the day andthe year. They owe theirpopularity to simplicity. Thesun-path diagram is used in thistext and is described in moredetail.

The sunpath diagram is aprojection of the hemisphere ofthe sky. The observer isassumed to be in the centre ofthis hemisphere and the sun totravel on the surface of thehemisphere. There are twotypes of projections used toobtain sun-path diagrams. Thef i rs t i s a stereographicprojection of the hemisphereonto a horizontal circle. This isthe most common projectionand is most useful in visualizingthe movement of the sun

10.3 From tables:

10.4 Experimental

methods:

10.5 Sun-path diagrams:

across the sky. See figure 10.The hemisphere can also beprojected onto a verticalsu r f ace . Th i s g i ve s anorthogonal sun-path diagramuseful in the analysis of shadingangles, glare and diffuse lightfrom the sky. See figure 11.

10

Figure 9: The solarscope.

Figure 10: Stereographic sunpath diagram for latitude 0.°

11

m a k e t h e n e c e s s a r ycalculations and present theresults graphically, sometimeseven in the form of plots. Suchprograms are now available onmicrocomputers and arebecoming more popular.

A good alternative is the use ofalmanacs where the necessarysolar angles are tabled. Thesetables undergo minor revisionsyearly.

Complex and lengthy researchon the sun-earth relationship iso f t e n c a r r i e d o u texperimentally using theheliodon, the solarscope orsome other device. See figure9. These studies are carried outon models and are verypopular in teaching.

T h e s e a r e g r a p h i c a lr ep re sen t a t i on s o f t hemovement of the sun acrossthe sky throughout the day andthe year. They owe theirpopularity to simplicity. Thesun-path diagram is used in thistext and is described in moredetail.

The sunpath diagram is aprojection of the hemisphere ofthe sky. The observer isassumed to be in the centre ofthis hemisphere and the sun totravel on the surface of thehemisphere. There are twotypes of projections used toobtain sun-path diagrams. Thef i rs t i s a stereographicprojection of the hemisphereonto a horizontal circle. This isthe most common projectionand is most useful in visualizingthe movement of the sun

10.3 From tables:

10.4 Experimental

methods:

10.5 Sun-path diagrams:

across the sky. See figure 10.The hemisphere can also beprojected onto a verticalsu r f ace . Th i s g i ve s anorthogonal sun-path diagramuseful in the analysis of shadingangles, glare and diffuse lightfrom the sky. See figure 11.

across the sky. See figure 10.The hemisphere can also beprojected onto a verticalsu r f ace . Th i s g i ve s anorthogonal sun-path diagramuseful in the analysis of shadingangles, glare and diffuse lightfrom the sky. See figure 11.

Fig

ure

11:O

rtho

gona

lsun

path

diag

ram

for

latit

ude

0.°

12

Figure 12: The overheated period for Zaria shown on the sunpath diagram.Shading this part of the sky gives no underheating and partial overheating.

Figure 13: The overheated period for Zaria shown on the sunpath diagram.Shading this part of the sky gives no overheating and partial underheating.

11. Superimposing

the sun-shading

periods.

The date and the time whenshading should start and stopshould be marked on the sun-path diagram: these pointsshould be joined and theenclosed area shaded. In doingthis there are usually instanceswhere the sun passes over thesame part of the sky at differenttimes requiring differentshading. It is left to the designert o c h o o s e b e t w e e noverheating, underheating or alittle of both. See figure 10.

The shaded area represents theposition of the sun in the skywhen shading is needed. Thesun-shading device should beso designed that it will blockthis part of the sky. Ther e q u i r e d g e o m e t r y i sdetermined using a shadowangle protractor.

The date and the time whenshading should start and stopshould be marked on the sun-path diagram: these pointsshould be joined and theenclosed area shaded. In doingthis there are usually instanceswhere the sun passes over thesame part of the sky at differenttimes requiring differentshading. It is left to the designert o c h o o s e b e t w e e noverheating, underheating or alittle of both. See figure 10.

The shaded area represents theposition of the sun in the skywhen shading is needed. Thesun-shading device should beso designed that it will blockthis part of the sky. Ther e q u i r e d g e o m e t r y i sdetermined using a shadowangle protractor.

The shadow angle protractor isused to determine thehorizontal and vertical shadingangles of the shading device.See appendix A.7 and A.11.There are two types, one foreach of the projections of thehemisphere, either onto ahorizontal or vertical surface.The shading angles can bedetermined for only oneorientation at a time. Thus if weare designing shading devicesfor a building with elevationsfacing N-E, S-E, S-W and N-W,we must take the fourorientations one by one andestablish the shading angles.This gives us four sets ofhorizontal and vertical shadingangles.

It is common to find that theshading mask defined by theseangles do not cover therequired portion of the sky.Some areas are left uncoveredwhile other areas are coveredunnecessarily. The designershould choose such angles thatwill be optimal.

13

Figure 14: Orthogonal shadow angle protractor.

Figure 15: Stereographic shadow angle protractor.

The date and the time whenshading should start and stopshould be marked on the sun-path diagram: these pointsshould be joined and theenclosed area shaded. In doingthis there are usually instanceswhere the sun passes over thesame part of the sky at differenttimes requiring differentshading. It is left to the designert o c h o o s e b e t w e e noverheating, underheating or alittle of both. See figure 10.

The shaded area represents theposition of the sun in the skywhen shading is needed. Thesun-shading device should beso designed that it will blockthis part of the sky. Ther e q u i r e d g e o m e t r y i sdetermined using a shadowangle protractor.

12. The Shadow

Angle Protractor.

The shadow angle protractor isused to determine thehorizontal and vertical shadingangles of the shading device.See appendix A.7 and A.11.There are two types, one foreach of the projections of thehemisphere, either onto ahorizontal or vertical surface.The shading angles can bedetermined for only oneorientation at a time. Thus if weare designing shading devicesfor a building with elevationsfacing N-E, S-E, S-W and N-W,we must take the fourorientations one by one andestablish the shading angles.This gives us four sets ofhorizontal and vertical shadingangles.

It is common to find that theshading mask defined by theseangles do not cover therequired portion of the sky.Some areas are left uncoveredwhile other areas are coveredunnecessarily. The designershould choose such angles thatwill be optimal.

The shadow angle protractor isused to determine thehorizontal and vertical shadingangles of the shading device.See appendix A.7 and A.11.There are two types, one foreach of the projections of thehemisphere, either onto ahorizontal or vertical surface.The shading angles can bedetermined for only oneorientation at a time. Thus if weare designing shading devicesfor a building with elevationsfacing N-E, S-E, S-W and N-W,we must take the fourorientations one by one andestablish the shading angles.This gives us four sets ofhorizontal and vertical shadingangles.

It is common to find that theshading mask defined by theseangles do not cover therequired portion of the sky.Some areas are left uncoveredwhile other areas are coveredunnecessarily. The designershould choose such angles thatwill be optimal.

14

Figure 16: Example of horizontal shading devices with thesame shading mask.

Figure 17: Example of horizontal shading devices with thesame shading mask.

13. Examples of Shading Devices.

The horizontal and vertical shading angles onlygive an indication of the required geometry ofthe shading device. The design of the actualshading device is based on structural andaesthetic factors and several designs can bemade in conformity with the shading angles.One important decision is whether to use asingle large element or several small elements.See figures 18, 17 and 18. Large elements areusually made of concrete while small elementsmay be made from various metals, plastics andwood. The shading devices may be designed as

The horizontal and vertical shading angles onlygive an indication of the required geometry ofthe shading device. The design of the actualshading device is based on structural andaesthetic factors and several designs can bemade in conformity with the shading angles.One important decision is whether to use asingle large element or several small elements.See figures 18, 17 and 18. Large elements areusually made of concrete while small elementsmay be made from various metals, plastics andwood. The shading devices may be designed as

adjustable and the need for a view out is oftenimportant. A great challenge to an architect isposed by aesthetics. A good design should befunctional, structural and reflect our culture.Examples of sunshading devices on existingbuildings (located at Ahmadu Bello University,Zaria) are shown in plate 1.

15

Figure 18: Examples of shading masks for vertical shadingdevices.

Plate 1: Examples of sunshading devices on existingbuildings.

The horizontal and vertical shading angles onlygive an indication of the required geometry ofthe shading device. The design of the actualshading device is based on structural andaesthetic factors and several designs can bemade in conformity with the shading angles.One important decision is whether to use asingle large element or several small elements.See figures 18, 17 and 18. Large elements areusually made of concrete while small elementsmay be made from various metals, plastics andwood. The shading devices may be designed as

adjustable and the need for a view out is oftenimportant. A great challenge to an architect isposed by aesthetics. A good design should befunctional, structural and reflect our culture.Examples of sunshading devices on existingbuildings (located at Ahmadu Bello University,Zaria) are shown in plate 1.

adjustable and the need for a view out is oftenimportant. A great challenge to an architect isposed by aesthetics. A good design should befunctional, structural and reflect our culture.Examples of sunshading devices on existingbuildings (located at Ahmadu Bello University,Zaria) are shown in plate 1.

16

14. Tests and Exercises.

1. Explain how solar heat can be regulated for thepurpose of achieving comfort in a tropicalhouse.

2. Describe three types of sun-shading devices.

3. Describe the steps involved in the design ofsun-shading devices for composite climates.

4. Describe how sun-shading periods areobtained from basic climatic data.

5. Sketch the details of the shadings devicesmade of the following materials:

a. Steel

b. Concrete

c. Timber

d. Plastic

6. Describe the types and geometries of sun-shading devices.

7. Describe how sun-shading periods are super-imposed on sun-path diagrams.

Evans, M. (1980). Housing, Climate andComfort. The Architectural Press, London.

Givoni, B. (1976). Man, Climate AndArchitecture. Second Edition. Applied SciencePublishers Ltd., London.

Harkness, E.L. and Mehta, M.L. (1978). SolarRadiation Control In Buildings. Applied SciencePublishers, London.

Koenigsberger, O.H., Ingersoll, T.G., Mayhew,A. and Szokolay, S.V. (1974). Manual of TropicalHousing And Building, Part I, Climatic Design.Longman, London.

Markus, T.A. and Morris, E.N. (1980). Buildings,Climate and Energy. Pitman International,London.

Ogunsote, O.O. (1986). "MOTOLA, STRESS andSHADE -Educational Software for TropicalCountries". Paper Presented at The Seminar OnComputer Aids: Computers and Climatic DataHeld at British Research Station, Garston,

15. References.

1. Explain how solar heat can be regulated for thepurpose of achieving comfort in a tropicalhouse.

2. Describe three types of sun-shading devices.

3. Describe the steps involved in the design ofsun-shading devices for composite climates.

4. Describe how sun-shading periods areobtained from basic climatic data.

5. Sketch the details of the shadings devicesmade of the following materials:

a. Steel

b. Concrete

c. Timber

d. Plastic

6. Describe the types and geometries of sun-shading devices.

7. Describe how sun-shading periods are super-imposed on sun-path diagrams.

Evans, M. (1980). Housing, Climate andComfort. The Architectural Press, London.

Givoni, B. (1976). Man, Climate AndArchitecture. Second Edition. Applied SciencePublishers Ltd., London.

Harkness, E.L. and Mehta, M.L. (1978). SolarRadiation Control In Buildings. Applied SciencePublishers, London.

Koenigsberger, O.H., Ingersoll, T.G., Mayhew,A. and Szokolay, S.V. (1974). Manual of TropicalHousing And Building, Part I, Climatic Design.Longman, London.

Markus, T.A. and Morris, E.N. (1980). Buildings,Climate and Energy. Pitman International,London.

Ogunsote, O.O. (1986). "MOTOLA, STRESS andSHADE -Educational Software for TropicalCountries". Paper Presented at The Seminar OnComputer Aids: Computers and Climatic DataHeld at British Research Station, Garston,

England. 10-11 June.

Olgyay, A. (1953). Shading and InsolationMeasurement of Models. University of TexasPress, Austin.

Olgyay, V. (1963). Design With Climate -Bioclimatic Approach To ArchitecturalRegionalism. Princeton University Press,Princeton, New Jersey.

Olgyay, V. and Olgyay, A. (1957). Solar Controland Shading Devices. Princeton UniversityPress, Princeton, New Jersey.

Petherbridge, P. (1969). Sunpath Diagrams andOverlays for Solar Heat Gain Calculations.HMSO, London.

Pleijel, G. (1956). "The Little Sundial". In:Orengrundsgabtan 10, Vol. VI. Stockholm,Sweden.

Prucnal-Ogunsote, B. and Ogunsote, O.O.(1988). "COLDHOT -A Design Aid for Multi-Index Thermal Stress Analysis". In: ArchitecturalScience Review, Vol. 31.3, pp 99-106. Sydney,Australia.

White, B.G. (1962). "Aids to The Design ofShading Devices For Latitudes 4 Degrees Northto 12 Degrees North". In: West African BuildingResearch Institute Research Note 6. Accra,Ghana.

England. 10-11 June.

Olgyay, A. (1953). Shading and InsolationMeasurement of Models. University of TexasPress, Austin.

Olgyay, V. (1963). Design With Climate -Bioclimatic Approach To ArchitecturalRegionalism. Princeton University Press,Princeton, New Jersey.

Olgyay, V. and Olgyay, A. (1957). Solar Controland Shading Devices. Princeton UniversityPress, Princeton, New Jersey.

Petherbridge, P. (1969). Sunpath Diagrams andOverlays for Solar Heat Gain Calculations.HMSO, London.

Pleijel, G. (1956). "The Little Sundial". In:Orengrundsgabtan 10, Vol. VI. Stockholm,Sweden.

Prucnal-Ogunsote, B. and Ogunsote, O.O.(1988). "COLDHOT -A Design Aid for Multi-Index Thermal Stress Analysis". In: ArchitecturalScience Review, Vol. 31.3, pp 99-106. Sydney,Australia.

White, B.G. (1962). "Aids to The Design ofShading Devices For Latitudes 4 Degrees Northto 12 Degrees North". In: West African BuildingResearch Institute Research Note 6. Accra,Ghana.